All references cited in this specification, and their references, are incorporated by reference herein where appropriate for teachings of additional or alternative details, features and/or technical background.
Disclosed are methods to control slow and fast scan image bar output defects from a raster output bar (ROB) assembly to provide wide format imaging capability.
The use of addressable image bars as an imaging device in electrophotographic printing machines is known. An image bar is a construct utilizing imaging components such as liquid crystals or light emitting diodes to guide or direct light rays to from images. The commonly used image bars are linear substrates having an effective length equivalent to the width of the standard letter size documents, e.g., 8½ inches. It is also known that the longer the image bar length, the greater the difficulty of manufacturing and the greater the cost. The yield of these types of bars decreases exponentially with increased pixel density in active areas in a linear direction.
In order to obtain an image bar of an increased length in order to accommodate larger size documents, such as engineering drawings with widths up to 36 inches for example, one or more image bars of relatively shorter lengths are linearly aligned in a staggered orientation to form together an image bar of effectively increased length. However, these bars, in addition to being linearly aligned physically, also need to be optically aligned with their outputs focused to a common line at a photoreceptor. Even after all the alignments have been performed prior to the installation of the image bar in the machine, further in-machine adjustments, sometime in the field, are required, which result in down-time and costly maintenance. There is a need for methods to alleviate problems associated with alignment and adjustment of image bars by executing certain mechanical mounting and adjustment strategies on the manufacturing floor prior to delivering the image bar to the field.
A commonly used image bar assembly in an electrophotographic copier/printer combination is described in U.S. Pat. No. 5,260,718 as shown in FIG. 1. The multifunction machine 10 shown in the Figure incorporates an imaging system 20 with image bar assemblies 30 and 30′. Copying function is provided by the imaging system 20, while the printing function is provided by imaging systems 30 and 30′ comprising image bar assemblies 35 and 35′ and their associated lens system 40 and 40′. In either the copying or printing mode, the final output may be printed on a printer 50 as shown in FIG. 1.
In copying mode, a document 13 is transported across the surface of platen 15 by a commonly used CVT (Continuous Velocity Transport) means (not shown). The document is incrementally illuminated by illumination from a pair of light sources 25 and 25′ energized by power supply 75 shown in FIG. 1. Light sources may comprise mercury lamps, fluorescent lamps, LEDs or a light source and a reflector. Light is reflected downward 23 and is imaged by Selfoc™ lens array (SLA) 20 onto a photoreceptor 55 (FIG. 1) on the surface of drum 53 creating a line by line exposure of the document and forming a latent image. As is known, printer 50 includes a series of process stations through which the photoreceptor drum 53 passes beginning with the image station 60 where the latent electrostatic image is formed. Drum 53 moves past development station 63, transfer station 65 where the image is transferred to paper and fused, to cleaning station 67, and to corona charging station 69 where the photoreceptor is charged.
When print mode is selected, imaging systems 30 and 30′ are enabled and subsequently controlled by signals from systems controller 70. Imaging systems 30 and 30′ comprise bar assemblies 35 and 35′ and associated Selfoc™ lens array (LSA) 40 and 40′, which are optically aligned along center line 37 and 37′, respectively. The two sets of components aligned along center lines 37 and 37′ form an angle θ and are sufficiently displaced from each other in their process direction to accommodate the copier imaging system 20 as shown in FIG. 1.
Light sources 25 and 25′ illuminate assemblies 35 and 35′, respectively. Bar assemblies 35 and 35′ shown in FIG. 1 comprise liquid crystal type image bars although other types of image bars may also be used, such as LED image bars addressed by appropriate control means. Image bar 35 contains two liquid crystal image bars 35-a, 35-c and image bar 35′ contains the other two complementary bars 35′-b, 35′-d. Image bars 35 and 35′ are arranged to form staggered linear as shown in FIG. 2. Each image bar has two offset rows of linear liquid crystal pixels. The transmissive state of each image bar is determined by selective application of a voltage to a plurality of electrodes on the image bar substrate. Bar control circuit 73 energizes the appropriate electrodes in response to digitized bit-mapped data input representing document information typically sent from a charge coupled device or from a computer and stored in controller memory. Bar control circuitry 73 is described in U.S. Pat. No. 5,207,718, which is incorporated herein by reference in its entirety, and will not be discussed any further here in order not to unnecessarily obscure the significant aspects of the present disclosure.
Each bit of data is polarized (“1” or “0”) to indicate whether the picture elements “pixels” it represents is to be printed black or white. Depending upon the individual liquid crystal shutter activation, image bars 35-a, 35′-b, 35-c, 35′-d selectively pass light through apertures 31 and 31′ to a pair of linear gradient index lens arrays 40, 40′, such as Selfoc™ SLA 12 lenses manufactured by Nippon Sheet Glass Company. The lenses image the light outputs (as two linear arrays of dots) from the staggered arrays as two lines at the photoreceptor surface.
It will be understood from the configuration shown in FIG. 2 that by staggering the image bars, and by using appropriately longer known gradient index lens arrays, images can be formed on the photoreceptor as being the sum of the length of each modulated image bar formed in the linear arrays. It will also be apparent that proper registration of the image bar will have to take place in the process and scan direction to ensure proper overlap at the ends of the bar to accommodate the required “stitching” of the several focused bar images. Referring to FIG. 3 there is shown a side perspective view of FIG. 1 showing three of the bars (35-a, 35′-b, 35-c) beneath light source 25. The Selfoc™ lens arrays have been omitted for clarity of description. The registration of the image bars in the process direction requires that: (1) the portions of the scan line projected from bar 35′-b align with the correct positions of scan lines projected from bars 35-a and 35-c, and (2) that the projected pixels do not overlap or leave a gap. As shown in FIG. 3 the raster formatted input data is recovered and stored in data buffer 80, located in bar control 73 shown in FIG. 1, and then read out in proper sequence to the three bars. It is evident that the data must be divided into three columns and directed to each of the three bars. Since the bars are multiplexed, i.e., each possesses two offset rows 90, 95 of pixels, with both energized at the same time and since these odd and even rows are offset, the data supplied are similarly offset. In order to obtain this offset, the data is read out of memory displaced by this offset, as shown. The data path is shown by reference numeral 100 while the optical merging direction is indicated by 110. Odd bits 120 and even bits 130 are allocated in buffer 80 as shown schematically in FIG. 3 where the displacement 140 of rows is the same as in the image bar. The raster line direction is shown by arrow 150.
The associated driving circuits and the functional representation of the image bars are described in U.S. Pat. No. 5,260,718 referenced above. Procedures for registration of the image bars in the scan direction are illustrated. Concerns related to overlapping of the bars are discussed. It is nevertheless experienced in the field that there can still be fast scan image bar output defects resulting from poor pixel stitching at the overlapping ends of the bars. Correction for these defects require in-machine adjustments in the field resulting in down-time and costly maintenance. What is needed is a method to fix the defects at the factory prior to the installation of the bars in the machine so that no further in-machine adjustments may be required in the field.